Cationic direct-penetrating dyes have long been known in hair tinting products. In oxidative dyeing systems, which during the dyeing process simultaneously lighten the natural hair melanin, in particular nitro and azo dyes are used, because most other types of dyes cannot withstand the oxidation process.
It is known to use particular azacyanines for the surface treatment of optical recording media.
Surprisingly, it has been discovered that particular cationic azacyanine dyes enable coloring to be carried out into the blue and blue-green ranges, and that, depending on the substitution pattern, they are oxidation-stable and can thus also be used in oxidative dyeing systems.